World War 2 was over 60 years ago and the Japanese took the first shot. War with Germany was inevitable if we fought the Japanese due to treaties between the two countries (and in fact we declared war on Germany after it had declared war on us). Nearly everyone who was alive at the time is dead and their views do not necessarily reflect their descendants'... Citing reasons and attitudes towards the war by people who are gone is not an excellent argument for why someone should support you, now.
The UN cannot do other than cave in because it is not an independent entity with its own military. Additionally, the makeup of the permanent members of the Security Council virtually guarantees that it's impossible to get anything militarily significant done - the member's interests are too diverse.